Burner control apparatus



United States Patent 3,221,799 BURNER CONTROL APPARATUS William B. Hamelink and Carl E. Swanson, Minneapolis, Minn., assignors t0 Honeywell Inc., a corporation of Delaware Filed Feb. 27, 1964, Ser. No. 347,935 4 Claims. (Cl. 15828) Our invention is concerned with an improved burner control apparatus and particularly with a program type burner control apparatus in which a timer is provided to sequentially control a plurality of electrical switch means, the switch means being adapted to be connected to the components of the fuel burner unit to program the fuel burner unit from a standby condition, through a prepurge period and a trial-for-ignition period, to a run condition. More particularly, our invention is concerned with a unique arrangement for providing an extended prepurge period and for additionally insuring that the ignition period is not instituted until certain components of the fuel burner unit are in a proper condition for optimum trial-for-ignition.

As is well known in the prior art, it is desirable to program large fuel burner installations so as to insure safe transition from a standby to a run condition. In the standby condition, the components of the fuel burner unit are for the most part deenergized and it is necessary to safely bring the burner unit through a transition where a main flame is established at a main burner. Furthermore, in installations of this type, the rate of firing of the main burner may be controlled by means responsive to demand for heat, this means being, for example, a damper controller to control the fiow of combustion air to the fire box, and an arrangement to modulate the fuel flow of a main fuel valve to change the supply of fuel to the main fuel burner as the damper is changed, to maintain the proper fuel-to-air ratio. We have chosen to show, in the preferred embodiment of our invention, the control of only a damper. However, it is recognized that it is within the teachings of our invention to utilize a modulating valve to be controlled in much the same fashion as the damper of our preferred embodiment. Considering generally the teachings of the prior art, the prepurge period is initiated by energization of a blower to purge the fire box of fumes or unburned fuel. During this prepurge period the damper is moved to the high fire position allowing the maximum amount of air to flow through the fire box. In some cases it may be desirable to maintain the damper fully open, that is in the high fire position, during the standby period. In any event, the damper is in the high fire position during a portion of the prepurge period.

Immediately following the prepurge period, the program burner control institutes a trial-for-ignition period. In accordance with the teachings of the prior art, the damper is controlled to institute movement to the low fire position during the prepurge period so as to insure that the damper will be at a low fire position prior to the institution of the trial-for-ignition period.

Our invention is concerned with the particular manner in which the damper motor is controlled as related to the program of the fuel burner unit. Specifically, the inventive concept of our structure resides in the arrangement whereby the damper motor begins its movement to low fire position immediately prior to the end of a particular program period, for example, the prepurge period. The damper motor requires a given time interval to move from the high fire to the low fire position and, as we control the damper motor, it will not be at the low fire position at the end of the prepurge period. Therefore, we provide an arrangement to interrupt the programming of the burner and to reinstitute the programming of the burner, to move into the trial-for-ignition period, only ice when the damper motor has reached the low fire position. In this manner, we not only insure that the damper motor must be at the low fire position before the trial-for-ignition period can be instituted, but we likewise obtain an extended prepurge period in which the damper is fully open for the major portion of the prepurge period, and in which the time of the prepurge period is determined not only by the program burner control, but also by the movement of the damper actuator, the damper actuator itself acting as a timer as it moves the damper from the high fire position to the low fire position.

In the preferred embodiment of our invention, we show a program burner control of the type having a plurality of cam operated switches. These cam operated switches are controlled from a small synchronous motor which drives a cam shaft at a uniform speed, the cam shaft carrying a number of cams. In order to obtain accurate switching by virtue of the cams, it is necessary that the cam rotate at an optimum rate. This optimum rate determines, to a practical extent, the prepurge time which can be provided. If too long a prepurge time is attempted by use of this structure, then the switching which follows the prepurge time takes place with a relatively small rotation of the cams and the required switching is difficult to achieve with accuracy and reliability. With the construction of our invention, since we rely on the timing of the damper actuator itself, we are able to select cam contours and rotation speeds of the cam to provide the optimum in reliable and accurate switching of the switches which are effective to program the fuel burner unit.

While we have chosen to use the terms high fire and low fire to describe a full open or a full'closed condition, it is within the teachings of our invention to utilize an arrangement in which the condition may not be full open or full closed, and define conditions at the ends of a range of conditions.

Our invention will be apparent to those skilled in the art upon reference to the following specification, claims, and drawings, of which:

FIGURE 1 is a schematic representation of our invention, and

FIGURE 2 is a bar graph showing the manner of operating the cam operated timer switches.

Referring to FIGURE 1, reference numeral 10 designates generally a fuel burner unit having a pilot burner 11 with its associated pilot valve 12, a main burner 13 with its associated main Valve 14, an ignition electrode 15 connected to an ignition transformer 16, and a blower 17 connected to an air flow conduit 18 having a damper 19, the damper position being controlled by a damper actua tor 20. The damper is shown in the low fire position, the dotted position 21 being the high fire position allowing maximum air flow to the fire box. Flame within the fire box is detected by a photocell 22 connected to the input of a flame detector 23, whose output constitutes a flame relay designated 2R. Flame 2R is provided with three switches designated 2R1, 2R2, and 2R3.

Damper actuator 20 includes a pair of coils 24 and 25 which are connected in an electrical energizing circuit arrangement, such that with coil 24 energized damper 19 moves to the high fire position and with coil 25 energized, as shown in FIGURE 1, the damper moves to the low fire position. Energization of coils 24 and 25 is effected, during the running period of the fuel burner unit, by means of a damper controller 26. This damper controller includes a movable switch blade 27 movable between fixed contacts 28 and 29 to energize the coils 24 and 25 respectively. Energization of the coils 24 and 25 is also programmed by means of the timer switches T1, T2, T3 and T4.

Reference numeral 30 designates a timer T. Timer T is a synchronous mot-or which is connected to rotate, at

a uniform speed, a plurality of contoured cams, each of the switches of the timer having a cam surface to control the timer switch in the manner disclosed in FIGURE .2. Timer T is provided with 12.switches, labeled T1 through T12 inclusive.

Also associated in an electrical circuit arrangement to control fuel burner unit is a main burner relay 1R having the switches 1R1, 1R2, 1R3 and 1R4.

In circuit with relay IR is a saftey cutout device 31 having a heater 32 and a bimetal actuator 33. As is well known, a timer period of energization of heater 32 is effective to cause the bottom end of bimetal 33 to Warp to the right to thus release a switch blade 34 to open and latch in the open position a normally closed switch 35. Safety cutout device 31 may be manually reset, by means not shown.

A further relay 3R is provided having a single switch 3R1. This relay functions to control energization of blower 17.

Referring now specifically to the operation of the apparatus of FIGURE 1, the apparatus is shown in the standby condition wherein operating voltage is applied to power line conductors 40 and 41. Damper 19 is in the low fire position by virtue of energization of coil 25 by way of a circuit which can be traced from conductor 41 through coil 25, timer switch T4 and timer switch T2 to conductor 40.

A call for operation of fuel burning unit 10 is evidenced by closing of start switch 42. The closing of this switch completes an energizing circuit for relay 1R, this energizing circuit being traced from conductor 41 through switch 35- of a cutout device 31,-:the lower portion of the winding of relay 1R, heater 32, switch 2R3, timer switch T8, and start switch 42 to power line conductor 40. Energization of relay 1R causes its associated switches to be actuated.

Closing of switch 1R3 completes an energizing circuit for relay 3R, thus causing an energizing circuit for blower motor 17 to begin the purge period. It will be noted that at this time damper 17 is in the low fire position.

The closing of switch 1R3 also completes an energizing circuit for timer 30 through the timer operated switches T11 and T12. Thus, the programmed operation of burner unit 10 begins as timer 30 causes rotation of the cams controlling the various timer switches.

Upon reference to FIGURE 2 it can be seen that the first switching occurs at the three second interval when the timer switch T1 closes and timer switch T2 opens. The closing of timer switch T1 completes an energizing circuit for the high fire winding 24 of damper actuator 20. I This circuit can be traced from power line conductor 41 through winding 24 and switch T1 to power line conductor 40. The opening of switch T2 opens the energizing circuit for winding 25, above traced, and thus damper 19 begins its movement from the low fire position to the high fire position. Therefore, the quantity of air passing through the fire box to purge the fire box increases to a maximum value as the damper is positioned at the high fire position.

It should be mentioned that it may be desirable to control damper 19 in a manner to cause the damper to be at the high fire position during the standby period. In this case, the prepurge period is instituted with the damper fully open.

Again upon reference to FIGURE 2, it can be seen that at the four second interval timer switch T10 closes. The closing of timer switch T10 provides a shunt circuit around switch 1R3, and since timer switch T10 remains closed until the end of the time period of operation provided by timer 30, relay 3R will remain energized and switch 3R1 will remain closed to maintain continuous operation of blower motor 17.

At the 10 second interval, switch T8 opens. The opening of this switch opens the starting interlock which insures that the program for fuel burner unit- 10 may not begin unless the timer motor 30 is in the start position wherein switch T8 is closed. Operation of the burner control apparatus is maintained through the stop button 50 and through the switch 1R2.

At the 3'2 second interval, timer switch T1 opens and timer switch T2 closes. The operation of these switches again energizes the low fire winding 25 of damper actuator 20 to begin the movement of the damper from the high fire position to the low fire position. As shown in FIG- URE 2, the end of the purge period is at the 40 second interval and thus it can be seen that return of the damper motor to the low fire position is instituted eight seconds prior to the end of the purge period. Thus, a purge period is provided wherein the damper is maintained in the high fire position for a major portion of the purge period. Furthermore, the majority of the damper motor actuators require longer than eight seconds to return from the high fire to the low fire position. Normally, these motors require from 15 to 60 seconds to drive the damper between its two positions. As is apparent, operation of damper actuator 20 is effective as a second timing means to extend the purge period.

At the 35 second interval, timer switch T12 opens. Timer switch T12 is in series with the energizing circuit for timer motor 30 and therefore timer motor 30 is now deenergized. Thus, the program of the burner unit is interrupted and will not be reinstituted until the low fire interlock switch 51 associated with the damper actuator 20 is closed. This switch is closed only when the damper is in the low fire position and the additional time required for the damper actuator to move the damper to the low fire position extendsthe prepurge period, thus contributing to additional safety in the programming of the fuel burner unit from its standby condition to its run condition.

While we have chosen to show our invention in the environment of a complete program burner control apparatus, the detailed timer and switch construction provided to safely program the burner control form no part of our invention. As we have stated, our inventive concept is concerned with the manner of insuring that the damper is at the low fire position before the fuel burner unit can be programmed into the trial-for-ignition period, and to also accomplish this result in a manner which extends the purge period, the damper actuator additionally functioning as a timer to extend the actual purge period.

Completing the explanation of the apparatus of FIG- URE 1, at the 38 second interval timer switch T9 closes and this switch is effective to operatively energize the heater 32 of safety cutout device 31, this energization taking place only after the program has been reinstituted by the closing of switch 51.

At the 42 second interval, switch T7 closes and this switch energizes pilot valve 12 and ignition transformer 16 to begin the trial-for-ignition period.

At the 46 second interval, switch T12 again closes. At the 50 second interval, switch T6 opens and switch T5 closes. The opening of switch T6 is effective to deenergize pilot valve 12 and ignition transformer 16, but only in the event that the pilot flame has not been detected. Normally, pilot flame is detected and relay 2R is energized to close switches 2R1 and 2R2. Switch 2R1 is in series with main valve 14 and the closing of timer contact T5 provides an energizing circuit for this valve so that a main flame may be established at main burner 13. Energization of flame relay 2R also causes a switch 2R3 to open to deenergize heater 32 of safety cutoff device 31.

At the second interval switch T3 closes and switch T4 opens. These switches are connected in the circuit of damper actuator 20 and actuation of these switches places the damper actuator under control of damper controller 26.

At the second interval, switch T7 opens to deenergize pilot valve 12 and ignition transformer 16. At the second interval, switch T11 opens and this switch is effective to deenergize timer 3%, thus establishing the beginning of the run period. The run period continues until stop button 50 is actuated.

Opening of stop button 50 is effective to deenengize relay IR and to deenergize main valve 14 of fuel burner unit 10. Deenergization of relay 1R closes its switch 1R4 and completes an energizing circuit for timer motor 30 such that this motor begins to program the fuel burner unit back to the standby condition.

While we have disclosed what we believe to be the preferred embodiment of our invention, we intend the scope of this invention to be limited solely by the scope of the appended claims.

We claim as our invention:

1. In a program burner control having a motor driven timer to sequentially control a plurality of cam operated switch means adapted to be connected to a fuel burner unit to sequentially program the same from a standby condition through at least a prepurge period and a trialfor-ignition period to a run condition, the fuel burner unit including an air damper having an electrically energizable actuator effective to move the air damper between high fire and low fire positions, the movement between these positions requiring a given time interval, the improvement comprising:

first circuit means controlled by said switch means and adapted to be connected to the air damper actuator to provide a prepurge period with the damper in the high fire position and to institute a return of the air damper to low fire position at a timer prior to the end of the purge period, said time prior to the end of the purge period being less than the given time interval,

and second circuit means controlled by said switch means, and adapted to be controlled by the position of the damper, to interrupt operation of the motor driven timer until such time as the damper is in the low fire position, to thus institute the trial-for-ignition period after a prepurge time as determined by operation of the motor driven timer and by operation of the damper actuator.

2. In a timer driven program burner control for a burner having ignition means, a fuel valve, an air blower, and a slow acting actuator for an air damper which is movable between high fire and low fire positions, the burner control being adapted to provide a sequential program of a purge period for the burner wherein the air blower is energized with the air damper at high fire position, followed by a trial-for-ignitio-n period wherein the air blower is energized with the air damper at low fire position and the ignition means and a fuel valve are energized, the improvement comprising:

first timer controlled means adapted to be connected to the actuator of the air damper to begin movement of the same toward the low fire position immediately prior to the end of the purge period as determined by the burner control,

second timer controlled means connected to interrupt operation of the sequential program at a time subsequent to operation of said first timer controlled means and prior to the end of the purge period as determined by the burner control,

and third means adapted to be controlled by the air damper when in the low fire position to reinstitute the sequential program, the purge time thus being determined by operation of said second timer controlled means followed by an additional time as determined by the air damper actuator.

3. In a program burn-er control having a timer to sequentially control a plurality of electrical switch means which are adapted to be connected to the components of a fuel burner unit to program the fuel burner unit from a standby condition through a prepurge period and an ignition period to a run condition; the fuel burner unit including an air damper having actuating means requiring a given time interval to move the damper between high fire and low fire position, and having a low fire interlock switch which is actuated when the damper is in the low fire position; the burner control providing a prepurge period with the air damper in a high fire position; the improvement comprising:

first switching circuit means controlled by the timer and adapted to be connected to the air damper actuating means to institute a return of the air damper to a low fire position at a time interval prior to the end of the prepurge period, said time interval being less than the given time interval,

second switching circuit means controlled by the timer to interrupt operation of the timer at a time after the beginning of said timer interval and prior to the beginning of the ignition period,

and third switching circuit means adapted to be controlled by the low fire interlock switch and connected to subsequently energize the timer upon return of the air damper to low fire position.

4. In a program burner control having a timer to sequentially control a plurality of electrical circuit means which are connected to a fuel burner unit to program the fuel burner unit from a standby condition through a prepurge period .and an ignition period to a run condition; the fuel burner unit having an air blower and an air damper which is movable between minimum and maximum air fiow positions, the movement between these positions requiring a given time interval, the air damper including a low fire interlock switch which is actuated when the air damper is at the minimum air flow position; the control providing a prepurge period wherein the air blower is energized with the damper at the maximum air flow position and the air damper is moved from the maximum air flow position to the minimum air flow position prior to initiation of the ignition period; the improvement comprising:

first circuit means controlled by the timer and effective to institute a return of the air damper to the minimum air flow position at a time interval prior to the end of the prepurge period, the time interval prior to the end of the prepurge period being less than the given time interval,

second circuit means controlled by the timer and effective to interrupt operation of the timer after institu tion of the return of the air damper to the minimum air flow position,

and third circuit means adapted to be controlled by the low fire interlock switch to subsequently energize the timer upon return of the air damper to the minimum air flow position to thus reinstitute the program of the fuel burner unit.

References Cited by the Examiner UNITED STATES PATENTS 2,339,618 1/ 1944 Cra-go. 2,748,844 6/1956 Gilchrist 15828 X 2,808,209 10/ 1957 Bressler 2361 JAMES W. WESTHAVER, Primary Examiner. 

1. IN A PROGRAM BURNER CONTROL HAVING A MOTOR DRIVEN TIMER TO SEQUENTIALLY CONTROL A PLURALITY OF CAM OPERATED SWITCH MEANS ADAPTED TO BE CONNECTED TO A FUEL BURNER UNIT TO SEQUENTIALLY PROGRAM THE SAME FROM A STANDBY CONDITION THROUGH AT LEAST A PREPURGE PERIOD AND AS TRIALFOR-IGNITION PERIOD TO A RUN CONDITION, THE FUEL BURNER UNIT INCLUDING AN AIR DAMPER HAVING AN ELECTRICALLY ENERGIZABLE ACTUATOR EFFECTIVE TO MOVE THE AIR DAMPER BETWEEN HIGH FIRE AND LOW FIRE POSITIONS, THE MOVEMENT BETWEEN THESE POSITIONS REQUIRING A GIVEN TIME INTERVAL, THE IMPROVEMENT COMPRISING: FIRST CIRCUIT MEANS CONTROLLED BY SAID SWITCH MEANS AND ADAPTED TO BE CONNECTED TO THE AIR DAMPER ACTUATOR TO PROVIDE A PREPURGE PERIOD WITH THE DAMPER IN THE HIGH FIRE POSITION AND TO INSTITUTE A RETURN OF THE AIR DAMPER TO LOW FIRE POSITION AT A RIMER PRIOR TO THE END OF THE PURGE PERIOD, SAID TIME PRIOR TO THE END OF THE PURGE PERIOD BEING LESS THAN THE GIVEN TIME INTERVAL, AND SECOND CIRCUIT MEANS CONTROLLED BY SAID SWITCH MEANS, AND ADAPTED TO BE CONTROLLED BY THE POSITION OF THE DAMPER, TO INTERRUPT OPERATION OF THE MOTOR DRIVEN TIMER UNTIL SUCH TIME AS THE DAMPER IS IN THE LOW FIRE POSITION, TO THUS INSTIUTE THE TRIAL-FOR-IGNITION PERIOD AFTER A PREPURGE TIME AS DETERMINED BY OPERATION OF THE MOTOR DRIVEN TIMER AND BY OPERATION OF THE DAMPER ACTUATOR. 